Thanks for the replies!

The legs don't feel so hot... My knees started really bothering me towards the end of the ride too, so I definitely need some kind of fitting. I bet the saddle position is a bit off...

But, anyway, pains aside, I'm stunned that I did as well as I did. Average speed was around 10mph cause you can't go much faster than that with all the other bikes and pedestrians on the path anyway. Turned out to be the perfect speed for me to manage that distance!